1. HOW TO
＜今日
PostgreSQLアンカンファレンス＠東京
2015/05/30 (土)
河原 翔

2. => CREATE TABLE test AS SELECT
generate_series('2014-05-30 00:00:00'::timestamp,
'2015-05-30 23:59:59',
'1 second') col1;
=> SELECT count(*) FROM test WHERE col1 < '2015-05-30';
count
----------
31536000
=> SELECT count(*) FROM test WHERE col1 >= '2015-05-30';
count
-------
86400
=# SELECT now();
now
-------------------------------
2015-05-30 11:49:25.454168+09
前準備

3. => SELECT count(*) FROM test WHERE
to_char(col1, 'YYYYMMDD') <
to_char(now(),'YYYYMMDD');
count
----------
31536000
時間: 42716.271 ms
Aggregate (cost=798723.00..798723.01 rows=1 width=0)
-> Seq Scan on test
(cost=0.00..772371.00 rows=10540800 width=0)
Filter: (to_char(col1, 'YYYYMMDD'::text) <
to_char(now(), 'YYYYMMDD'::text))
< to_char(now(),'YYYYMMDD')

4. => SELECT count(*) FROM test WHERE col1 < CURRENT_DATE;
count
----------
31536000
時間: 13180.751 ms
Aggregate (cost=772191.53..772191.54 rows=1 width=0)
-> Seq Scan on test
(cost=0.00..693315.00 rows=31550610 width=0)
Filter: (col1 < ('now'::cstring)::date)
< CURRENT_DATE

5. => SELECT count(*) FROM test WHERE
col1 < date_trunc('day',now());
count
----------
31536000
時間: 12536.489 ms
Aggregate (cost=772122.00..772122.01 rows=1 width=0)
-> Seq Scan on test
(cost=0.00..693315.00 rows=31522801 width=0)
Filter: (col1 < date_trunc('day'::text, now()))
< date_trunc('day',now())

6. => WITH today AS (SELECT date_trunc('day',now()))
SELECT count(*) FROM test WHERE col1 < (TABLE today);
count
----------
31536000
時間: 5931.524 ms
Aggregate (cost=561555.04..561555.05 rows=1 width=0)
CTE today
-> Result (cost=0.00..0.01 rows=1 width=0)
InitPlan 2 (returns $1)
-> CTE Scan on today (cost=0.00..0.02 rows=1 width=8)
-> Seq Scan on test
(cost=0.00..535203.00 rows=10540800 width=0)
Filter: (col1 < $1)
WITH

7. => SELECT count(*) FROM test WHERE col1 < 'today'::date;
count
----------
31536000
時間: 3665.628 ms
Aggregate (cost=614079.53..614079.54 rows=1 width=0)
-> Seq Scan on test
(cost=0.00..535203.00 rows=31550610 width=0)
Filter: (col1 < '2015-05-30'::date)
< 'today'::date

8. => CREATE VIEW tview AS SELECT count(*) FROM test WHERE
col1 < 'today'::date;
=> SELECT definition FROM pg_views WHERE
viewname = 'tview';
-[ RECORD 1 ]-----------------------------------------
definition | SELECT count(*) AS count
| FROM test
| WHERE (test.col1 < '2015-05-30'::date);
※「'today'::date」部がviewが作成された日付固定になってしまう
【注意】'today'::dateはview不可

9. => CREATE INDEX ON test(col1);
=> SELECT
(SELECT count(*) FROM test) -
(SELECT count(*) FROM test WHERE
col1 >= 'today'::date) count;
count
----------
31536000
時間: 2259.013 ms
※「SELECT count(*) FROM test WHERE col1 < 'today'::date」では
INDEXは利用されない
【参考】INDEX